1. Field of the Invention
This invention relates to intumescent fire retardant coating compositions. Objects coated with such a composition are provided protection in case of a fire because in a fire the materials in the coating decompose and intumesce (bubble and foam) resulting in the formation of a non-flammable barrier which insulates the object from heat.
More particularly, this invention relates to water-based intumescent fire retardant coating compositions which contain a phosphate compound as a fire retardant additive.
2. Description of the Prior Art
It is well known that various phosphorus-containing compounds can be used as fire retardant additives in intumescent coating compositions. Although phosphate compounds which are relatively water-soluble, such as mono-ammonium ortho phosphate, have been used in these compositions, it has recently been discovered that improved durability of the coating is obtained when relatively water-insoluble phosphates are employed. Coatings with improved washability, water-resistance, moisture-resistance and weather-resistance are obtained when relatively water-insoluble phosphates are employed in the intumescent coating compositions.
Ammonium polyphosphates are disclosed as being useful as a fire retardant additive in intumescent coating compositions in U.S. Pat. No. 3,562,197, issued to Paul G. Sears et al on Feb. 9, 1971. These ammonium polyphosphates are described as substantially water-insoluble and are stated to be particularly useful in water-based paint formulations. These water-based compositions are said to generally comprise an aqueous dispersion of a binder and a carbonific, i.e., a carbon-yielding substance, in addition to the phosphate fire retardant material.
Substantially water-insoluble ammonium polyphosphates are also employed in intumescent coating compositions described in U.S. Pat. No. 3,513,114 issued to Frank J. Hahn et al on May 19, 1970. These compositions include a solvent plasticizer in addition to a binder, carbonific and the phosphate material.
In U.S. Pat. No. 4,009,137, issued to Franz-Josef Dany et al on Feb. 22, 1977, high molecular weight ammonium polyphosphates which are said to be very scarcely soluble in water are employed in intumescent flame-retardant coating compositions.
Substituted ammonium polyphosphates are disclosed as being useful as flame retardant additives in water-based coating compositions in U.S. Pat. No. 4,043,987, issued to Carmel R. Jolicoeur et al on Aug. 23, 1977. These polyphosphates are described as compounds based on ammonium polyphosphate having a proportion of its ammonium radicals substituted by an organic nitrogenous spumific agent containing "reactive nitrogen". The term "reactive nitrogen" refers to nitrogen in the form of amino, imino or isocyanate radicals. A spumific material is defined as one which, on heating, decomposes to give gaseous products required for the formation of a froth or foam. These substituted ammonium polyphosphate compounds are described as being substantially water-insoluble.
In U.S. Pat. No. 3,969,291 issued to Kozo Fukuba et al on July 13, 1976 there is described the use of a substantially water-insoluble amide polyphosphate condensate as a fire retardant additive in intumescent coating compositions which also contain a film-forming binder and a carbonific material.
Still another type of phosphate compound useful as a flame retardant in intumescent coating compositions is described in U.S. Pat. No. 3,914,193 issued to Robert G. Phessler et al on Oct. 21, 1975 wherein the use of a low viscosity crystalline form of melamine pyrophosphate is disclosed.
The use of the aforementioned substantially water-insoluble phosphate compounds in intumescent coating compositions results in compositions which have properties far superior to coating compositions containing water soluble ammonium phosphates.
However, an improvement in certain properties is desirable for intumescent coating compositions containing substantially water-insoluble phosphates. For example, viscosity stability problems, i.e., an increase in viscosity of the composition upon storage, have occurred in water-based intumescent coating compositions containing these phosphate compounds and it is desirable to improve the viscosity stability of these compositions.
It is therefore, an object of the present invention to provide aqueous intumescent fire retardant coating compositions which exhibit improved storage stability.
It is a further object of this invention to provide a method of stabilizing the viscosity of aqueous intumescent fire retardant coating compositions which contain certain substantially water-insoluble phosphorus-containing materials.
These and other objects will become apparent from the following detailed description.